Working out bullet drop in games, jump arcs, how fast you're going when you leave a platform.

It's usually simulations and things, they can use it to tell how things will react depending on the angle they're moving and how fast, can be used for space exploration, games, and other similar things that require knowledge of movement and curves. So even calculating an arc for a machine to throw a basketball into a net every single time.

Buying stocks. Take the derivative of a stock at a given time to see how fast it's going up or down.

Physics, for finding out where something is at any given time, with any given speed or acceleration.